DC—DC power converters are commonly used for supplying power to electronic devices and systems, such as power supply devices, computers, printers and imaging systems. Such DC—DC converters are available in a number of configurations for outputting a desired voltage from a source voltage, including a buck or step down converter (FIG. 1), a boost converter (FIG. 2), and a flyback converter (FIG. 3). FIG. 1 is a circuit diagram of a DC—DC buck converter 100 having an inductor 102, a capacitor 104, switches 106a and 106b, along with a rising cycle path 108a and falling cycle path 108b, for producing an output voltage Vout that is less than a source voltage Vin. FIG. 2 is a circuit diagram of a DC—DC boost converter 200 having an inductor 202, a capacitor 204, switches 206a and 206b, along with a rising cycle path 208a and falling cycle path 208b. FIG. 3 is a circuit diagram of a DC—DC flyback converter 300 having an inductor 302, a capacitor 304, switches 306a and 306b, along with a rising cycle path 308a and falling cycle path 308b. 
In order to effect control of DC—DC converter and voltage regulator circuits, accurate measurement of inductor current is necessary. A common approach for sensing an output inductor current in a buck converter (FIG. 1) utilizes a sensing resistor connected in series with the output inductor. The output inductor current is reconstructed as a differential voltage across the sensing resistor. The output voltage is then regulated with current mode control, where the sensed signal is used for output voltage feedback. An example of such a DC—DC converter with a sensing resistor is shown in U.S. Pat. No. 5,731,731. Other examples of direct sensing of inductor current for DC—DC converter control include those shown in U.S. Pat. Nos. 5,982,160 and 6,377,034. FIG. 4 is a circuit diagram of a conventional DC—DC buck converter 400 with a control circuit 402, a sensing circuit 404 and a sensing resistor 406. The sensing resistor value, however, must be sufficiently large in magnitude in order to keep the sensed signal above noise. A serious efficiency drawback results from power being unnecessarily dissipated by the sensing resistor.
Indirect sensing or deriving inductor current for DC—DC converter control is also available. Examples of indirect sensing of inductor current include those shown in U.S. Pat. No. 6,381,159 and U.S. Patent Application Publication No. US 2002/0074975. Although indirect sensing does not require a sensing resistor, a drawback is the requirement that internal nodes of the converter be tapped for internal voltages, which results in additional circuitry and signal pins.
There is thus a general need in the art for a system and method for inductor current control that can overcome the aforementioned shortcomings in the art. A particular need exists for a system and method for inductor current control in DC—DC converters that is efficient, and also minimizes power dissipation problems. A further need exists for a system and method for inductor current control in DC—DC converters with efficient and optimized circuit design.